Formation and Evolution of Mirror Mode Type Fluctuations in the Earth's Magnetosheath in Global Hybrid-Vlasov Simulations

We study mirror mode type waves in the magnetosheath using the global hybrid-Vlasov simulation code Vlasiator. Vlasiator solves for ions in 6-dimensional phase space using the Vlasov equation and for electrons as a massless charge-neutralizing fluid using the magnetohydrodynamic equations. The code is therefore able to capture the kinetic physics absent in global MHD simulations. We run Vlasiator in a 5-dimensional setup with a fully 3-dimensional velocity space and two-dimensional (equatorial) plane. We present results from several runs, with various interplanetary magnetic field directions, including a typical Parker spiral orientation as well as radial IMF. We investigate the formation, evolution and advection of the mirror modes in the magnetosheath. We also study how the wave field variations depend on the IMF cone angle. Simulation results indicate that the mirror mode type waves are generated behind the bow shock close to the foreshock edge. The waves then advect towards the quasi-perpendicular flanks of the magnetosheath. Additionally, we look at the evolution of the ion velocity distributions and how they depend on the mirror modes along streamlines in the magnetosheath. Finally, we compare our simulation results with observational data from the THEMIS spacecraft.